Density Of Stubby Spines Research Articles

Si-Ni-San alleviates early life stress-induced depression-like behaviors in adolescence via modulating Rac1 activity and associated spine plasticity in the nucleus accumbens.

Background: Early life stress (ELS) is a major risk factor for depression in adolescents. The nucleus accumbens (NAc) is a key center of the reward system, and spine remodeling in the NAc contributes to the development of depression. The Si-Ni-San formula (SNS) is a fundamental prescription for treating depression in traditional Chinese medicine. However, little is known about the effects of SNS on behavioral abnormalities and spine plasticity in the NAc induced by ELS. Purpose: This study aimed to investigate the therapeutic effect and the modulatory mechanism of SNS on abnormal behaviors and spine plasticity in the NAc caused by ELS. Methods: We utilized a model of ELS that involved maternal separation with early weaning to explore the protective effects of SNS on adolescent depression. Depressive-like behaviors were evaluated by the sucrose preference test, the tail suspension test, and the forced swimming test; anxiety-like behaviors were monitored by the open field test and the elevated plus maze. A laser scanning confocal microscope was used to analyze dendritic spine remodeling in the NAc. The activity of Rac1 was detected by pull-down and Western blot tests. Viral-mediated gene transfer of Rac1 was used to investigate its role in ELS-induced depression-like behaviors in adolescence. Results: ELS induced depression-like behaviors but not anxiety-like behaviors in adolescent mice, accompanied by an increase in stubby spine density, a decrease in mushroom spine density, and decreased Rac1 activity in the NAc. Overexpression of constitutively active Rac1 in the NAc reversed depression-related behaviors, leading to a decrease in stubby spine density and an increase in mushroom spine density. Moreover, SNS attenuated depression-like behavior in adolescent mice and counteracted the spine abnormalities in the NAc induced by ELS. Additionally, SNS increased NAc Rac1 activity, and the inhibition of Rac1 activity weakened the antidepressant effect of SNS. Conclusion: These results suggest that SNS may exert its antidepressant effects by modulating Rac1 activity and associated spine plasticity in the NAc.

Effects of heterozygous deletion of autism-related gene Cullin-3 in mice.

Autism Spectrum Disorder (ASD) is a developmental disorder in which children display repetitive behavior, restricted range of interests, and atypical social interaction and communication. CUL3, coding for a Cullin family scaffold protein mediating assembly of ubiquitin ligase complexes through BTB domain substrate-recruiting adaptors, has been identified as a high-risk gene for autism. Although complete knockout of Cul3 results in embryonic lethality, Cul3 heterozygous mice have reduced CUL3 protein, demonstrate comparable body weight, and display minimal behavioral differences including decreased spatial object recognition memory. In measures of reciprocal social interaction, Cul3 heterozygous mice behaved similarly to their wild-type littermates. In area CA1 of hippocampus, reduction of Cul3 significantly increased mEPSC frequency but not amplitude nor baseline evoked synaptic transmission or paired-pulse ratio. Sholl and spine analysis data suggest there is a small yet significant difference in CA1 pyramidal neuron dendritic branching and stubby spine density. Unbiased proteomic analysis of Cul3 heterozygous brain tissue revealed dysregulation of various cytoskeletal organization proteins, among others. Overall, our results suggest that Cul3 heterozygous deletion impairs spatial object recognition memory, alters cytoskeletal organization proteins, but does not cause major hippocampal neuronal morphology, functional, or behavioral abnormalities in adult global Cul3 heterozygous mice.

Effects of Cyclophosphamide and/or Doxorubicin in a Murine Model of Postchemotherapy Cognitive Impairment.

Postchemotherapy cognitive impairment, or PCCI, is a common complaint, particularly among breast cancer patients. However, the exact nature of PCCI appears complex. To model the human condition, ovariectomized C57BL/6J mice were treated intravenous weekly for 4 weeks with saline, 2 mg/kg doxorubicin (DOX), 50 mg/kg cyclophosphamide (CYP), or DOX + CYP. For the subsequent 10 weeks, mice were assessed on several behavioral tests, including those measuring spatial learning and memory. After sacrifice, hippocampal spine density and morphology in the dentate gyrus, CA1, and CA3 regions were measured. Additionally, hippocampal levels of total glutathione, glutathione disulfide, MnSOD, CuZnSOD, and cytokines were measured. Body weight decreased in all groups during treatment, but recovered post-treatment. Most behaviors were unaffected by drug treatment: Open field activity, motor coordination, grip strength, water maze and Barnes maze performance, buried food test performance, and novel object and object location recognition tests. There were some significant effects of CYP and DOX + CYP treatment during the initial test of home cage behavior, but these did not persist into the second and third test times. Density of stubby spines, but not mushroom or thin spines, in the dentate gyrus was significantly decreased in the DOX, CYP, and DOX + CYP treatment groups. There were no significant effects in the CA1 or CA3 regions. CuZnSOD levels were significantly increased in DOX + CYP-treated mice; other hippocampal antioxidant levels were unaffected. Most cytokines showed no treatment-related effects, but IL-1β, IL-6, and IL-12 were slightly reduced in mice treated with DOX + CYP. Although the animal model, route of exposure, and DOX and CYP doses used here were reflective of human exposure, there were only sporadic effects due to chemotherapeutic treatment.

Dendritic spines provide cognitive resilience against Alzheimer's disease.

Neuroimaging and other biomarker assays suggest that the pathological processes of Alzheimer's disease (AD) begin years prior to clinical dementia onset. However, some 30 to 50% of older individuals who harbor AD pathology do not become symptomatic in their lifetime. It is hypothesized that such individuals exhibit cognitive resilience that protects against AD dementia. We hypothesized that in cases with AD pathology, structural changes in dendritic spines would distinguish individuals who had or did not have clinical dementia. We compared dendritic spines within layer II and III pyramidal neuron dendrites in Brodmann area 46 dorsolateral prefrontal cortex using the Golgi-Cox technique in 12 age-matched pathology-free controls, 8 controls with AD pathology (CAD), and 21 AD cases. We used highly optimized methods to trace impregnated dendrites from bright-field microscopy images that enabled accurate 3-dimensional digital reconstruction of dendritic structure for morphologic analyses. Spine density was similar among control and CAD cases but was reduced significantly in AD. Thin and mushroom spines were reduced significantly in AD compared to CAD brains, whereas stubby spine density was decreased significantly in CAD and AD compared to controls. Increased spine extent distinguished CAD cases from controls and AD. Linear regression analysis of all cases indicated that spine density was not associated with neuritic plaque score but did display negative correlation with Braak staging. These observations provide cellular evidence to support the hypothesis that dendritic spine plasticity is a mechanism of cognitive resilience that protects older individuals with AD pathology from developing dementia. Ann Neurol 2017;82:602-614.

Phosphorylation of CYFIP2, a component of the WAVE-regulatory complex, regulates dendritic spine density and neurite outgrowth in cultured hippocampal neurons potentially by affecting the complex assembly.

Actin dynamics is a critical mechanism underlying many cellular processes in neurons. The heteropentameric WAVE-regulatory complex (WRC), consisting of WAVE, CYFIP1/2, Nap, Abi, and HSPC300, is a key regulator of actin dynamics that activates the Arp2/3 complex to initiate actin polymerization and branching. The WRC is basally inactive because of intermolecular interactions among the components, which can be modulated by bindings of phospholipids and Rac1, and phosphorylations of WAVE and Abi. However, the phosphorylation of other components of WRC and their functional significance remain largely unknown. To address this issue, we focused on CYFIP1/2, in which we found two brain-specific phosphorylation sites (S582 of CYFIP2 and T1068/T1067 of CYFIP1/2) from a publicly available phosphoproteome database. To understand their functional effects, we overexpressed wild-type, phospho-blocking, or phospho-mimetic mutants of CYFIP2 in cultured hippocampal neurons, and found that only T1067A CYFIP2 decreased the density of stubby spines. Moreover, overexpression of wild-type CYFIP2 increased neurite length, but T1067A did not exert this effect. To understand the mechanism, we modeled CYFIP2 phosphorylation in the crystal structure of WRC and found that T1067 phosphorylation could weaken the interaction between CYFIP2 and Nap1 by inducing conformational changes of CYFIP2 α-helical bundles. In the co-immunoprecipitation assay, however, wild-type, T1067A, and T1067E CYFIP2 showed similar interaction levels to Nap1, suggesting that T1067 phosphorylation alone is not sufficient to disrupt the interaction. Considering that the activation of WRC requires disassembly of the complex, our results suggest that T1067 phosphorylation, together with other factors, could contribute toward the activation process.

Differential dendritic remodeling in prelimbic cortex of male and female rats during recovery from chronic stress

Chronic stress produces differential dendritic remodeling of pyramidal neurons in medial prefrontal cortex of male and female rats. In males, this dendritic remodeling is reversible. However, the timeline of recovery, as well as the potential for reversibility in females, is unknown. Here, we examined dendritic recovery of pyramidal neurons in layer II-II of prelimbic cortex in male and female rats following chronic restraint stress (3h/day for 10days). Dendritic morphology and spine density were analyzed immediately following the cessation of stress, or following a 7- or 10-day recovery period. Chronic stress produced apical dendritic retraction in males, which was coupled with a decrease in the density of stubby spine on apical dendrites. Further, following a 10-day recovery period, the morphology of neurons from stressed rats resembled that of unstressed rats. Male rats given a 7-day recovery period had apical dendritic outgrowth compared to unstressed rats. Immediately after cessation of stress, females showed only minimal dendritic remodeling. The morphology of neurons in stressed females resembled those of unstressed rats following only 7days of recovery, at which time there was also a significant increase in stubby spine density. Males and females also showed different changes in baseline corticosterone concentrations during recovery. These findings not only indicate that dendritic remodeling in prelimbic cortex following chronic stress is different between males and females, but also suggest chronic stress induces differential hypothalamic–pituitary–adrenal axis dysregulation in males and females. These differences may have important implications for responses to subsequent stressors.

BA11 FKBP5 expression levels correlate with dendritic spine density in postmortem PTSD and controls

Genetic variants of the immunophilin FKBP5 have been implicated in susceptibility to post-traumatic stress disorder (PTSD) and other stress-related disorders. We examined the relationship between mushroom, stubby, thin and filopodial spine densities measured with Golgi staining and FKBP5 gene expression in the medial orbitofrontal cortex (BA11) in individuals diagnosed with PTSD and normal controls (n = 8/8). ANCOVA revealed PTSD cases had a significantly elevated density of stubby spines (29%, P < 0.037) and a trend for a reduction in mushroom spine density (25%, p < 0.082). Levels of FKBP5 mRNA were marginally elevated in the PTSD cases (z = 1.94, p = 0.053) and levels correlated inversely with mushroom (Spearman's rho = −0.83, p < 0.001) and overall spine density (rho = −0.75, p < 0.002) and directly with stubby spine density (rho = 0.55, p < 0.027). These data suggest that FKBP5 may participate in a cellular pathway modulating neuronal spine density changes in the brain, and that this pathway may be dysregulated in PTSD.

Changes of Dendritic Spine Density and Morphology in the Superficial Layers of the Medial Entorhinal Cortex Induced by Extremely Low-Frequency Magnetic Field Exposure

In the present study, we investigated the effects of chronic exposure (14 and 28 days) to a 0.5 mT 50 Hz extremely low-frequency magnetic field (ELM) on the dendritic spine density and shape in the superficial layers of the medial entorhinal cortex (MEC). We performed Golgi staining to reveal the dendritic spines of the principal neurons in rats. The results showed that ELM exposure induced a decrease in the spine density in the dendrites of stellate neurons and the basal dendrites of pyramidal neurons at both 14 days and 28 days, which was largely due to the loss of the thin and branched spines. The alteration in the density of mushroom and stubby spines post ELM exposure was cell-type specific. For the stellate neurons, ELM exposure slightly increased the density of stubby spines at 28 days, while it did not affect the density of mushroom spines at the same time. In the basal dendrites of pyramidal neurons, we observed a significant decrease in the mushroom spine density only at the later time point post ELM exposure, while the stubby spine density was reduced at 14 days and partially restored at 28 days post ELM exposure. ELM exposure-induced reduction in the spine density in the apical dendrites of pyramidal neurons was only observed at 28 days, reflecting the distinct vulnerability of spines in the apical and basal dendrites. Considering the changes in spine number and shape are involved in synaptic plasticity and the MEC is a part of neural network that is closely related to learning and memory, these findings may be helpful for explaining the ELM exposure-induced impairment in cognitive functions.

Blockade of BDNF signaling turns chemically‐induced long‐term potentiation into long‐term depression

Long-term potentiation (LTP) is accompanied by increased spine density and dimensions triggered by signaling cascades involving activation of the neurotrophin brain-derived neurotrophic factor (BDNF) and cytoskeleton remodeling. Chemically-induced long-term potentiation (c-LTP) is a widely used cellular model of plasticity, whose effects on spines have been poorly investigated. We induced c-LTP by bath-application of the N-methyl-d-aspartate receptor (NMDAR) coagonist glycine or by the K(+) channel blocker tetraethylammonium (TEA) chloride in cultured hippocampal neurons and compared the changes in dendritic spines induced by the two models of c-LTP and determined if they depend on BDNF/TrkB signaling. We found that both TEA and glycine induced a significant increase in stubby spine density in primary and secondary apical dendrites, whereas a specific increase in mushroom spine density was observed upon TEA application only in primary dendrites. Both TEA and glycine increased BDNF levels and the blockade of tropomyosin-receptor-kinase receptors (TrkRs) by the nonselective tyrosine kinase inhibitor K-252a or the selective allosteric TrkB receptor (TrkBR) inhibitor ANA-12, abolished the c-LTP-induced increase in spine density. Surprisingly, a blockade of TrkBRs did not change basal spontaneous glutamatergic transmission but completely changed the synaptic plasticity induced by c-LTP, provoking a shift from a long-term increase to a long-term depression (LTD) in miniature excitatory postsynaptic current (mEPSC) frequency. In conclusion, these results suggest that BDNF/TrkB signaling is necessary for c-LTP-induced plasticity in hippocampal neurons and its blockade leads to a switch of c-LTP into chemical-LTD (c-LTD).

The synaptic adhesion molecule SynCAM 1 contributes to cocaine effects on synapse structure and psychostimulant behavior.

Drugs of abuse have acute and persistent effects on synapse structure and addiction-related behaviors. Trans-synaptic interactions can control synapse development, and synaptic cell adhesion molecule (SynCAM) proteins (also named nectin-like molecules) are immunoglobulin adhesion proteins that span the synaptic cleft and induce excitatory synapses. Our studies now reveal that the loss of SynCAM 1 in knockout (KO) mice reduces excitatory synapse number in nucleus accumbens (NAc). SynCAM 1 additionally contributes to the structural remodeling of NAc synapses in response to the psychostimulant cocaine. Specifically, we find that cocaine administration increases the density of stubby spines on medium spiny neurons in NAc, and that maintaining this increase requires SynCAM 1. Furthermore, mushroom-type spines on these neurons are structurally more plastic when SynCAM 1 is absent, and challenging drug-withdrawn mice with cocaine shortens these spines in SynCAM 1 KO mice. These effects are correlated with changes on the behavioral level, where SynCAM 1 contributes to the psychostimulant effects of cocaine as measured after acute and repeated administration, and in drug-withdrawn mice. Together, our results provide evidence that the loss of a synapse-organizing adhesion molecule can modulate cocaine effects on spine structures in NAc and increases vulnerability to the behavioral actions of cocaine. SynCAM-dependent pathways may therefore represent novel points of therapeutic intervention after exposure to drugs of abuse.

Influence of predator stress on the consolidation versus retrieval of long-term spatial memory and hippocampal spinogenesis

We have studied the influence of predator stress (30 min of cat exposure) on long-term (24 h) spatial memory and the density of spines in basilar dendrites of CA1 neurons. Predator stress occurred either immediately before water maze training (Stress Pre-Training) or before the 24 h memory test (Stress Pre-Retrieval). The Control (nonstress) group exhibited excellent long-term spatial memory and a robust increase in the density of stubby, but not mushroom, shaped spines. The Stress Pre-Training group had impaired long-term memory and did not exhibit any changes in spine density. The Stress Pre-Retrieval group was also impaired in long-term memory performance, but this group exhibited an increase in the density of stubby, but not mushroom, shaped spines, which was indistinguishable from the control group. These findings indicate that: (1) A single day of water maze training under control conditions produced intact long-term memory and an increase in the density of stubby spines in CA1; (2) Stress before training interfered with the consolidation of information into long-term memory and suppressed the training-induced increase in spine density; and (3) Stress immediately before the 24 h memory test trial impaired the retrieval of the stored memory, but did not reverse the training-induced increase in CA1 spine density. Overall, this work provides evidence of structural plasticity in dendrites of CA1 neurons which may be involved in the consolidation process, and how spinogenesis and memory are modulated by stress.